memccpy.c raw

   1  #include <string.h>
   2  #include <stdint.h>
   3  #include <limits.h>
   4  
   5  #define ALIGN (sizeof(size_t)-1)
   6  #define ONES ((size_t)-1/UCHAR_MAX)
   7  #define HIGHS (ONES * (UCHAR_MAX/2+1))
   8  #define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
   9  
  10  void *memccpy(void *restrict dest, const void *restrict src, int c, size_t n)
  11  {
  12  	unsigned char *d = dest;
  13  	const unsigned char *s = src;
  14  
  15  	c = (unsigned char)c;
  16  #ifdef __GNUC__
  17  	typedef size_t __attribute__((__may_alias__)) word;
  18  	word *wd;
  19  	const word *ws;
  20  	if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) {
  21  		for (; ((uintptr_t)s & ALIGN) && n && (*d=*s)!=c; n--, s++, d++);
  22  		if ((uintptr_t)s & ALIGN) goto tail;
  23  		size_t k = ONES * c;
  24  		wd=(void *)d; ws=(const void *)s;
  25  		for (; n>=sizeof(size_t) && !HASZERO(*ws^k);
  26  		       n-=sizeof(size_t), ws++, wd++) *wd = *ws;
  27  		d=(void *)wd; s=(const void *)ws;
  28  	}
  29  #endif
  30  	for (; n && (*d=*s)!=c; n--, s++, d++);
  31  tail:
  32  	if (n) return d+1;
  33  	return 0;
  34  }
  35